Three-dimensional MXene/BCN microflowers for wearable all-solid-state microsupercapacitors

Modified MXene (Ti 3 C 2 Tx) is attractive as a flexible electrode for wearable energy storage devices. In this work, a convenient and effective method was proposed to change the conventional 2D boron carbon nitride (BCN) nanosheets into three-dimensional 3D BCN microspheres that were obtained by tube furnace drying under N 2 flow and annealing. Then, the MXene/BCN microflowers were applied to all-solid-state flexible microsupercapacitors (MSCs) as a high-performance electrode material. It was found that the areal capacitance can reach up to 89 mF cm −2 for a single MSC under 0.5 mA cm −2 . Furthermore, the MSCs can achieve remarkable mechanical flexibility such that the capacitance will not be evidently decreased even after bending by up to 180°. In addition, 90.1% capacity retention was obtained even after 10 000 cycles and the highest energy density and power density reached 0.0124 mW h cm −2 (volumetric energy density of approximately 17.7 mW h cm −3 ) and 3.1 mW cm −2 (volumetric power density of approximately 4.5 W cm −3 ). These results demonstrate the synthesis of MXene/BCN composite materials with excellent power density and large scalability and can provide distinctive insights into high-performance flexible device storage systems. Illustration of the preparation of the MXene/BCN electrode. Left panel: synthesis of MXene/BCN. Right panel: design of a versatile MXene/BCN electrode for printing, the 2D pattern (top row) and the three-electrode system (bottom row).